Aortocoronary bypass graft surgery is a frequently employed therapeutic intervention in the management of coronary heart disease. It is well known, however, that the patency of such grafts can decrease progressively over time. The definitive confirmation of a graft's patency is selective angiography. This procedure is costly, invasive, and carries some degree of morbidity and mortality. Alternative noninvasive methods for evaluating graft patency have included thallium scans, doppler- echo, IV digital subtraction angiography, and computed tomography (CT). Of these alternatives only CT has achieved sufficient accuracy to warrant continued consideration as a noninvasive alternative to angiography. Nevertheless, CT methods are somewhat expensive, deliver an appreciable radiation dose to the heart, and require a significant learning curve if false negative and false positive evaluations are to be avoided. It is the aim of this proposal to develop a new noninvasive technique for the evaluation of graft patency, but one that is inexpensive, requires 1/10 of the radiation dose of a CT scan, and avoids problems of graft identification inherent in CT techniques by using a procedure that separates identification from graft evaluation. This new technique will use a small dedicated two- detector x-ray scanning system suitable for attachment to a cath lab fluoroscopic unit or a small portable x-ray generator. This scanning system will use x-ray scatter and x-ray induced fluorescence for the location and evaluation of by-pass grafts respectively. The aim of this proposal is to design, construct, test, and validate this new system. Testing and validation will be performed on mechanical models, animal models (canine), and humans.